docs: add Foreign Inline Show plugin documentation

Author: NoOne7135

adminforth/documentation/docs/tutorial/05-Plugins/15-ForeignInlineShow.md

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+
+Allows to add an inline show of connected foreign resource records on a adminforth show page.
+
+Foreign inline show plugin allows to display a show of items from a foreign table in the show view.
+
+## Usage
+
+
+Import plugin:
+
+```bash
+npm i @adminforth/foreign-inline-show --save
+```
+
+```ts title="./resources/adminuser.ts"
+import ForeignInlineShowPlugin from '@adminforth/foreign-inline-show';
+import { AdminForthResource, AdminForthResourceColumn } from 'adminforth';
+```
+
+
+In [Getting Started](<../001-gettingStarted.md>) we created a `'aparts'` resource which has a field `'realtor_id'`.
+This field refers to record from `'adminuser'` resource. To remind you, we configured this relation using `foreignResource` setting in the column configuration:
+
+```typescript title="./resources/apartments.ts"
+// 
+export default {
+  resourceId: 'aparts',
+  ...
+  columns: [
+    ...
+    {
+      name: 'realtor_id',
+      foreignResource: {
+        resourceId: 'adminuser',  // this means that aparts.realtor_id refers to primary key of 'adminuser' resource
+                              // this is Many-To-One relatin: many aparts can refer to one user
+      }
+    }
+  ],
+}
+```
+
+This means that we can display a show of user in the apartments show view.
+
+Add to your `'apartments'` resource configuration the plugin instance:
+
+```ts title="./resources/apartments.ts"
+{ 
+    ...
+    resourceId: 'aparts',
+    ...
+//diff-add
+    plugins: [
+//diff-add
+      new ForeignInlineShowPlugin({
+//diff-add
+        foreignResourceId: 'users',
+//diff-add
+      }),
+//diff-add
+    ],
+}
+```
+
+![alt text](ForeignInlineShow.png)
+
+> 👆 To make plugin work, the specified resource (defined with `foreignResourceId`) should have one (and only one) column that refers to the current resource on which you add a plugin.
+> In our case we add plugin to `adminuser` resource, so the `aparts` resource should have one column with `foreignResource.resourceId` equal to `adminuser` resourceId.